1. Field of This Invention
This invention relates to the field of life vests or life jackets and the process of and apparatus for preparing life jackets.
2. Prior Art
Difficulties are encountered when one attempts to insert an elastically bendable plate-shaped piece of foam plastic into a pocket of flexible material, which is fitted to the piece of foam plastic, through a slit-shaped opening formed at an edge of the pocket where the periphery of the pocket opening is shorter than the periphery of the cross section of the piece of foam plastic when positioned perpendicular to the direction of insertion. The problems are especially encountered whenever the material is relatively stiff in texture and the circumference of the opening of the pocket is considerably smaller than that of the cross-section of the piece of foam plastic (positioned perpendicular to the direction of introduction). Such is particularly the case when inserting closed-celled pieces of foam plastic into the pockets of lifesaving jackets since the pieces of foam plastic have a considerable resistance to flexure. This is so because the pieces of foam plastic are close-called, therefore being not very compressible, and have to be relatively thick in order to achieve the volume which is necessary for the required buoyancy in the water. The insertion of the pieces of foam plastic is also considerably complicated by the fact that the surface of foam plastic, especially the surface of close-called foam plastic, has considerable resistance or friction as it has a very large number of small indentations which adhere firmly to an adjacent surface even in the instance of little contact pressure.
In the production of life jackets and for the formation of the pockets, each of which is to receive one piece of foam plastic, the pieces made of flexible material are first sewn together over a large part of their periphery. The small residual peripheral part forms a slit-shaped opening through which the piece of foam plastic is inserted. The residual peripheral part is then sewn together. In the case of the production process for life jacekts, the slot-shaped opening is formed on a straight side of the pocket, but is sometimes shorter that than side. Each end of the slit is at a distance from the adjacent end (the adjacent corner) of such straight side of the pocket. At the same time the slit-like opening is naturally shorter than the diemsnion of the piece of foam plastic corresponding to this side of the pocket. The difference between the circumference of the slit-like opening (i.e., double the length of the slit) and the circumference of the cross section on the corresponding side of the piece of foam plastic is even more considerable because the thickness of the foam also constitutes a part of the cross sectional circumference. Such quite naturally complicates the insertion of the piece of foam plastic. However the opening, which does not extend to the corners, can after insertion therein of the piece of foam plastic be sewn up more easily and quickly, hence more economically, than an opening which extends from one corner to the other. This is so because the existing part of the seam has already been guided around the corners of the pocket in which the corresponding corners of the piece of foam plastic are then located. In order to understand the easier and quicker sewing up of the opening, one must realize that the piece of foam plastic totally fills the pocket. If the seam had not been sewn around the corners, in order to have the edges of the slit cover each other so they could be sewn together, it would be necessary to deform the piece of foam plastic somewhat at the adjacent end. That is cumbersome because of the limited volume-elasticity of the close-celled foam plastic. But such problem is not encountered whenever the already existing seam has already been completed around the corners and already extends partly in the direction in which it must be completed in order to close the opening. The advantage of the facilitated closing of the opening is considerable, but hardly prevailed hitherto, because it was expensive, cumbersome and time consuming to insert the piece of foam plastic into the pocket through the small opening.